#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
int main()
{
	int arr[] = { 1,2,3,4,1,2,3 };
	int i = 0;
	int ret = 0;
	for (i = 0; i < sizeof(arr) / sizeof(arr[0]); i++)
	{
		ret ^= arr[i];
	}
	printf("%d", ret);
	return 0;
}